An ideal vaccine for the prevention of cholera is not yet available. Previous work by the investigator resulted in development of an attenuated live oral cholera vaccine, V. cholerae CVD103-HgR. This vaccine confers strong protective immunity against experimental challenge with virulent V. cholerae O1 after a single dose. However, this vaccine is limited in that it does not protect against the El Tor biotype as well as it does against the classical biotype and it offers no protection against the recently emerged V. cholerae O139 serogroup. Additional vaccine candidates have been developed by deleting genes encoding cholera toxin and other toxins of V. cholerae but these other strains produce varying amounts of diarrhea and non-diarrheal symptoms such as headache, fever, abdominal cramps, and malaise in many individuals. The proposed project will develop additional vaccine candidates for O139 V. cholerae by deletion of specific genes encoding toxins and other virulence factors from a toxigenic O139 parent strain and by transferring genes encoding important antigens of O139 to CVD 103-HgR. In addition, the investigator will study previously uncharacterized virulence factors that may be involved in the reactogenicity of vaccine candidates other than CVD 103-HgR. Additional vaccine candidates for O139 V. cholerae will be constructed by deletion of specific genes encoding toxins and other virulence factors from a toxigenic O139 parent strain and by transferring genes encoding important antigens of O139 to CVD 103-HgR. In addition, previously uncharacterized virulence factors that may be involved in the reactogenicity of vaccine candidates other than CVD 103-HgR will be studied. The investigator has recently cloned the genes for the OmpU outer membrane protein and the phospholipase of V. cholerae. He has shown that OmpU has adhesive properties and that altered expression of this protein may be responsible for the diminished intestinal colonization which is associated with diminished vaccine reactogenicity. The phospholipase may be involved in a recently recognized inflammatory response to V. cholerae infection. The phospholipase may act on epithelial cells and break down membrane phospholipids, thereby releasing chemoattractants to trigger an inflammatory response that may be involved in vaccine reactogenicity.